A video information system for recording and playback of video information has been described by Clemens in U.S. Pat. Nos. 3,842,194 and 3,842,217. According to this system, video, audio and color information is recorded in the form of geometric variations in the bottom of a spiral groove in a surface of a disc. Disc replicas made of an insulating material, such as vinyl, are coated with a conductive metal layer as a first electrode of a capacitor and then with a dielectric film. A metal tipped stylus acts as a second electrode of the capacitor. The stylus monitors changes in capacitance between the stylus and the metal film on the record as these geometric variations pass beneath the stylus upon rotation of the grooved disc to effect recovery of signals occupying a band width of at least several megahertz and converted back to video information suitable for display by a television monitor.
In this system, the metal stylus is separated from the conductive disc surface by a thin dielectric layer. In order to produce good quality recordings, this dielectric layer must be uniform in depth and composition, thin enough so that the minute dimensional variations in the groove can be detected in an exact manner, yet without pinholes which would cause shorts due to metal-to-metal contact during playback. In addition, the dielectric coating must be strong enough to withstand repeated passes of the stylus without damage to or undue wear of the stylus, the disc coating or the metallized disc surface beneath. Thus the dielectric coating must have lubricant properties as well as high strength. The dielectric surface must also be resistant to degradation due to light or oxidation and must be inert with respect to the material from which the disc is made and to the metal coating. Still further, the dielectric layer must be able to be applied in a rapid and simple manner, suitable for mass production techniques.
U.S. Pat. No. 3,843,399 describes a dielectric polymeric coating applied by a glow discharge technique. This coating, while it can be applied as a uniform, pinhole-free, conformal film, does not have the lubricant properties required and the stylus wear rate is extremely high. The polymeric dielectric layer thus must be coated with a lubricant film. A suitable lubricant film has been described in U.S. Pat. No. 3,833,408 for example. These lubricants are methyl alkyl siloxanes which have the formula ##STR1## wherein R is an alkyl group, preferably from 4 to 20 carbon atoms and x is an integer.
It would be desirable, in the interest of cost reduction for making these disc recordings, to be able to apply a single dielectric layer which would have all of the properties required.